Use of specific volatile fatty esters in petrol engines in order to reduce emissions

ABSTRACT

The invention relates to the use of esters of volatile fatty acids, such esters having a number of carbon atoms between 4 and 8, in a fuel for a petrol engine in order to reduce the emissions of nitrogen oxides, unburned hydrocarbons and particles of petrol engines.

The present invention relates to improving the quality of petrol, and in particular to reducing the emissions of nitrogen oxides, unburnt hydrocarbons, and particles, of petrol engines.

Today, petrol engines are preferred to diesel engines because they emit fewer harmful substances. They are intended to be used in much greater part. However, they nonetheless emit nitrogen oxides, unburnt hydrocarbons, and particles which are dangerous for the environment and for human and animal health.

At present, no satisfactory solution has been proposed which makes it possible to reduce all these emissions of the petrol engines.

The object of the invention is to find a product that can be used on an industrial scale and is capable of reducing emissions of nitrogen oxides, unburnt hydrocarbons, and particles, of petrol engines.

In order to achieve said object, the present invention proposes using specific esters.

Esters have already been used in fossil fuels. In particular, the esters of vegetable oils or animal fats have been mixed with gas oil. These esters are referred to as “long” esters (16 to 20 carbon atoms per molecule) or “average” esters (8 to 16 carbon atoms per molecule).

However, said esters do not make it possible to achieve the object of the invention, since they cannot be used in a mixture with petrol owing to insufficient volatility. Moreover, no ester has hitherto been used in a mixture with petrol in order to significantly reduce the emissions.

However, according to the invention, the use of one or more “short” esters of volatile fatty acids comprising a number of carbon atoms per molecule of between 4 and 8, in petrol, surprisingly makes it possible to reduce the emissions of nitrogen oxides, unburnt hydrocarbons, and particles, of petrol engines. Moreover, the use according to the invention advantageously makes it possible to simultaneously increase the octane number of the petrol.

Other features and advantages will become clear from the following detailed description of the invention.

Definitions

Within the meaning of the invention, “volatile fatty acid” means a monocarboxylic fatty acid having an aliphatic chain of one to six carbon atoms (formic, acetic, propionic, butyric, valeric and caproic acids), or one of the isomers thereof.

Within the meaning of the invention, “fuel” or “fuel for petrol engine” means a fuel which can operate a petrol engine, with or without particular adjustment of the engine, preferably an engine comprising at least petrol and optionally other constituents.

Within the meaning of the invention, “short volatile fatty acid ester” or “short ester” or “short ester of volatile fatty acids” means an ester formed by the reaction of a volatile fatty acid with an alcohol such that the ester comprises a number of carbon atoms of between 4 and 8.

Within the meaning of the invention “unburnt hydrocarbons” means components comprising exclusively carbon and hydrogen atoms, emitted by an engine. The unburnt hydrocarbons comprise methane CH₄ and the other unburnt hydrocarbons which are also referred to as “non-methanogenic hydrocarbons.”

Within the meaning of the invention, “octane number of the petrol” means, in a general manner, either the RON octane number, or the MON octane number.

Within the meaning of the invention, “research octane number” of the petrol or “RON number” means a number measured in accordance with the method NF EN ISO 5164:2005.

Within the meaning of the invention, “motor octane number” of the petrol or “MON number” means a number measured in accordance with the method NF EN ISO 5163:2005.

Within the meaning of the invention, “incorporation of a compound at a rate of x % by volume into the fuel” (in particular “incorporation of esters at a rate of x % by volume into the fuel”) means the formation, by any suitable means, of a mixture, by adding a volume of x % of the compound (for example esters) and a volume of 1-x % of petrol, and possible other additives present in the fuel. The fuel is thus formed by x % of the compound, and 1-x % of petrol and possible other additives.

Within the meaning of the invention “nitrogen oxides” means compounds comprising only atoms of oxygen and nitrogen, the most common in the emissions of engines being nitrogen monoxide NO and nitrogen dioxide NO₂.

“Number of carbons” of an ester or an alkane means the number of carbon atoms of one molecule of ester or alkane.

Within the meaning of the invention, “use of a compound at a rate of x % by volume of fuel” (in particular “use of esters at a rate of x % by volume of fuel”) means the use, in a petrol engine, of a fuel formed by the compound (for example one or more esters), petrol, and possible other additives, obtained by incorporation of the compound at a rate of x % by volume into the fuel. The fuel is thus formed by x % of the compound, and by 1-x % of petrol and possible other additives.

DETAILED DESCRIPTION OF THE INVENTION

The invention therefore relates to the use of at least one volatile fatty acid ester, said ester comprising a number of carbons of between 4 and 8, in a fuel for petrol engines, in order to reduce the emissions of nitrogen oxide and unburnt hydrocarbons, and preferably also in order to reduce the particles from the petrol engines.

Preferably, volatile fatty acid ester(s) comprising a number of carbons of between 4 and 8 are used, at a rate of at least 15% by volume of fuel formed by the ester(s), the petrol, and the possible other constituents, and even more preferably at a rate of at least 20%, preferably at a rate of at least 30%, and, according to a particularly suitable embodiment, at a rate of at least 50%. These ratios make it possible to achieve particularly effective results in terms of reducing the emissions of nitrogen oxides, unburnt hydrocarbons, and particles, of petrol engines.

The short ester(s) of volatile fatty acids used according to the invention may be selected from among the following esters: ethyl acetate, ethyl propionate, ethyl butyrate, ethyl valerate, ethyl hexanoate, propyl acetate, propyl propionate, propyl butyrate, propyl valerate, butyl acetate, butyl propionate, butyl butyrate, and the mixtures thereof.

The ester(s) used according to the invention are preferably obtained, entirely or in part, from biomass (volatile fatty acids of biomass origin and/or alcohols of biomass origin), according to any suitable method. They can in particular be obtained, entirely or in part, and preferably entirely, by fermentation of biomass (anaerobic fermentation for the volatile fatty acids, and alcoholic or aceto-butanol fermentation for the alcohols), i.e. by esterification of volatile fatty acids of biomass origin by alcohols of biomass origin. The volatile fatty acids can also be obtained from carbon dioxide or monoxide in a microbial fuel cell. Thus, the esters of volatile fatty acids comprising a number of carbons of between 4 and 8 may be obtained entirely or in part by esterification of volatile fatty acids of biomass origin by alcohols of biomass origin, or by esterification of volatile fatty acids produced from carbon dioxide or monoxide, in a microbial fuel cell, by alcohols (the alcohols may be of biomass origin or otherwise).

The esters of volatile fatty acids comprising a number of carbon atoms of between 4 and 8, in a fuel for a petrol engine, make it possible in particular and can be used so as to:

-   -   reduce the emission of nitrogen oxides by the petrol engines by         at least 20% of the rate of incorporation of the ester into the         fuel, or for example a reduction of at least 10% for 50% of         esters incorporated into the fuel (the emission of nitrogen         oxides may in particular be measured according to a method that         meets the requirements of the European regulation Euro 6, i.e.         regulation 459/2012 of 29 May 2012); and/or     -   reduce the emission of unburnt hydrocarbons by the petrol         engines by at least 20% of the rate of incorporation of the         ester into the fuel, or for example a reduction of at least 10%         for 50% of esters incorporated into the fuel (the emission of         unburnt hydrocarbons may in particular be measured according to         a method that meets the requirements of the European regulation         Euro 6, i.e. regulation 459/2012 of 29 May 2012);     -   and optionally to reduce the mass and number of particles         emitted per kilometer travelled, by the petrol engines, by at         least 25% of the rate of incorporation of the ester into the         fuel, or for example a reduction of at least 12.5% for 50% of         esters incorporated into the fuel (mass and number of particles         emitted per kilometer travelled, by the petrol engines, may in         particular be measured according to a method that meets the         requirements of the European regulation Euro 6, i.e. regulation         459/2012 of 29 May 2012).

Advantageously, the use according to the invention can also make it possible, in addition to the uses set out above, to:

-   -   increase the “research” octane number of the petrol by at least         2 points, preferably at least 3 points; and/or     -   increase the “motor” octane number of the petrol by at least 2         points, preferably at least 3 points.

These uses are very advantageous and make it possible to obtain a fuel which has a significantly reduced negative impact on the environment compared with the petrols currently used.

In combination with the short esters, it is possible to use other petrol additives, so as to increase the effects of the esters of volatile fatty acids and to act in synergy. It is in particular possible to add one or more alkanes, of which the number of carbon atoms of the molecule is between 4 and 10, to the petrol, in addition to the short esters of volatile fatty acids, in order to optimize the combustion. Said alkanes may be of petroleum origin or originate from a biomass. Preferably, the alkanes used according to the invention originate from a biomass. Said alkanes, in combination with the short esters, make it possible to reduce the emissions of nitrogen oxide and unburnt hydrocarbons even further. Said alkanes are preferably selected from octane, iso-octane, decane, and mixtures thereof. Indeed, said alkanes tend to improve the combustion of the mixture.

Said alkanes are preferably used at an incorporation rate of between 0 and 50% by volume of fuel. They are preferably produced from volatile fatty acids originating from anaerobic fermentation of biomass by “Kolbe” electrolysis.

In addition to short esters, petrol, and possible alkanes, it is possible to add, in combination, one or more other product(s) into the fuel, said products being selected from:

-   -   additives which improve the octane number, such as         organometallic compounds such as MMT and Ferrocene, or ethers         such as ETBE or TAME, or aromatic hydrocarbons such as toluene,     -   additives which improve lubrication, such as average esters such         as hexyl valerate, hexyl caproate, or longer esters,     -   products which reduce the combustion temperatures, such as         nitrogen compounds such as amines, urea or ammonia, possibly         mixed with water,     -   alcohols such as isopropanol, butanol, hexanol, or octanol,     -   and mixtures thereof.

Said additives make it possible in particular, and in combination with the esters of volatile fatty acids, to further reduce the emissions of nitrogen oxides and unburnt hydrocarbons, or indeed to improve other operating parameters of the petrol engines.

The invention will now be illustrated by examples and test results.

EXAMPLES Example 1

Use of 15% ethyl butyrate in RON 95 petrol (85% petrol—15% ethyl butyrate)

Example 2

Use of 30% ethyl butyrate in RON 95 petrol (70% petrol—30% ethyl butyrate)

Example 3

Use of 30% ethyl butyrate and 10% iso-octane in RON 95 petrol (60% petrol—30% ethyl butyrate—10% iso-octane)

Example 4

Use of 50% ethyl butyrate and 20% iso-octane in RON 95 petrol (30% petrol—50% ethyl butyrate—20% iso-octane)

Test Results

The aim of the tests carried out is to evaluate the effect of using esters of volatile fatty acids comprising a number of carbon atoms of between 4 and 8, in a fuel comprising petrol, on the emissions of nitrogen oxides, unburnt hydrocarbons, and particles, of petrol engines, and also on the octane number of the petrol.

The emissions tests were carried out on an EP6 monocylindrical spark-ignition engine using the compositions of examples 1 to 4, in comparison with RON 95 petrol alone.

The RON octane number measurements were carried out in a laboratory, according to regulatory standards of French fuel specifications.

The operating protocol of the tests is described in the following: 8 engine points per mixture of fuel implemented to cover a use representative of a driving cycle:

-   -   1500 rpm, 4, 8, 12 bar and maximum AlP     -   2000 rpm, 4, 8, 12 bar and maximum AlP         For each engine point, the spark advance is optimized in order         to obtain a maximum AlP (average indicated pressure). The         richness of the mixture is adjusted to 1. It is necessary to         wait a few minutes in order to stabilize the engine thermal and         the exhaust emissions. The particles are analyzed on a PBS         PEGASOR probe.

The results relating to the emissions of nitrogen oxide are set out in Table 1.

TABLE 1 Average emissions of nitrogen Percentage reduction oxides (ppm) compared with RON 95 petrol RON 95 4428.5 Example 1 4280.8 3.3% Example 2 4138.8 6.5% Example 3 4023.3 9.1% Example 4 3839.7 13.3%

The results relating to the emissions of unburnt hydrocarbons are set out in Table 2.

TABLE 2 Average emissions of unburnt Percentage reduction hydrocarbons (ppm) compared with RON 95 petrol RON 95 3070.2 Example 1 2832.8 7.7% Example 2 2779.5 9.5% Example 3 2761.5 10.1% Example 4 2695.7 12.2%

The results relating to the emissions of particles are set out in Table 3.

TABLE 3 Average emissions of Percentage reduction particles (mass in mg/m³) compared with RON 95 petrol RON 95 0.01 Example 1 undetectable Example 2 undetectable Example 3 undetectable Example 4 undetectable

The results relating to the octane number are set out in Table 4.

TABLE 4 RON octane number RON 95 95.1 Example 1 98.1

These results indeed show that the use of short esters of volatile fatty acids makes it possible to simultaneously:

-   -   reduce the emissions of nitrogen oxides     -   reduce the emissions of unburnt hydrocarbons     -   reduce the emissions of particles.         It also makes it possible to very significantly increase the         octane number of the petrol. 

1. A method for reducing emissions of nitrogen oxides and unburnt hydrocarbons by a petrol engine, the method comprising adding at least one ester of a volatile fatty acid to a fuel for the petrol engine, wherein the volatile fatty acid is a mono-fatty acid having an aliphatic chain of one to six carbon atoms or one of the isomers thereof, and wherein said ester comprises a number of carbons of between 4 and
 8. 2-15. (canceled)
 16. The method of claim 1, wherein the method also reduces emission of particles by the petrol engine.
 17. The method of claim 1, wherein the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8 are used at a rate of at least 15% by volume of fuel, the fuel being formed by the petrol, the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8, and by possible other constituents.
 18. The method of claim 1, wherein the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8 are used at a rate of at least 30% by volume of fuel.
 19. The method of claim 17, wherein the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8 are used at a rate of at least 50% by volume of fuel.
 20. The method of claim 1, wherein the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8 are selected from among the following esters: ethyl acetate, ethyl propionate, ethyl butyrate, ethyl valerate, ethyl hexanoate, propyl acetate, propyl propionate, propyl butyrate, propyl valerate, butyl acetate, butyl propionate, butyl butyrate, and the mixtures thereof.
 21. The method of claim 1, wherein the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8 are obtained entirely or in part by esterification of volatile fatty acids of biomass origin by alcohols of biomass origin, or by esterification of volatile fatty acids produced from carbon dioxide or monoxide, in a microbial fuel cell, by alcohols of biomass origin or otherwise.
 22. The method of claim 1, wherein adding the ester to the fuel reduces the emission of nitrogen oxides by the petrol engines by at least 20% of the rate of incorporation of the esters in the fuel formed by the petrol, the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8, and possible other constituents.
 23. The method of claim 1, wherein adding the ester to the fuel reduces the emission of unburnt hydrocarbons by the petrol engines by at least 20% of the rate of incorporation of the esters in the fuel formed by the petrol, the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8, and possible other constituents.
 24. The method of claim 1, wherein adding the ester to the fuel reduces the emission of particles by the petrol engines by at least 25% of the rate of incorporation of the esters in the fuel formed by the petrol, the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8, and possible other constituents.
 25. The method of claim 1, wherein the method further comprises adding to the fuel at least one alkane having a chain length of between 4 and 10 carbon atoms in order to optimize combustion.
 26. The method of claim 25, wherein the alkane or alkanes is/are selected from octane, iso-octane, decane, and the mixtures thereof.
 27. The method of claim 25, wherein the alkane or alkanes are of petroleum origin or obtained from a biomass.
 28. The method of claim 25, wherein the alkane or alkanes are used at a rate of between 0 and 50% by volume of fuel formed by the petrol, the ester or esters of volatile fatty acids comprising a number of carbons of between 4 and 8, the alkane or alkanes having a chain length of between 4 and 10 carbon atoms, and possible other constituents.
 29. The method of claim 1, wherein the method further comprises adding one or more other products to the fuel, said products being selected from: additives that improve the octane number, additives that improve lubrication, products that reduce the combustion temperature, alcohols, esters comprising a number of carbons of greater than 8, ethers, and mixtures thereof. 